First off, before we do the usual IDO bigger=better it would be intelligent to determine which length Tyee we’re even talking about here?
With a 90, my guess is we’re probably talking about one of the 17 footers here. If that is the case, a 90 2 stroke is plenty for this rig. A 90 will drive this rig at more than adequate cruising speed.
The two strokes don’t suffer from the massive weight bloat that came into play with 4 strokes and they have more bottom end punch, so you don’t need to upsize by 20-30 HP just to overcome the added fat and slow response of a 4 stoke.
Another reason why more isn’t necessarily better in this vintage of boat/outboard is that carbed outboards are thirsty. And bigger is even thirstier.
In this vintage of rig, I think a 17 with a 90 would be a very nice rig if you can find one in good condition.
Grouse